The subject matter of the present invention relates generally to dump valves, and in particular to dump valves connected to the discharge port of a chemical reactor tank. The dump valve is self-cleaning and is provided with substantially vertical valve seat and valve plug sealing surfaces together with a sealing means for forming a liquid tight seal between such surfaces. As a result little material is deposited on the sealing surfaces since liquid flows off such surfaces due to gravity. In addition, any material deposited upon the surfaces is removed by the wiping action of such surfaces as they slide across each other during opening and closing of the valve. As a result, a reliable liquid tight seal is formed which is resistant to the pressure created by the liquid within the reactor tank, to high temperatures and to corrosive liquids such as that employed in the manufacture of polyvinyl chloride and other synthetic plastics.
In the manufacture of polyvinyl chloride and other polymeric products there are employed for converting the monomer to the polymer batch type reactors comprising a reactor tank or vessel fitted at the bottom with a discharge port and a communicating discharge conduit. During the reaction, the chemical liquids used for such reaction are contained in the vessel, and at the conclusion of the reaction the contents are discharged therefrom by operation of a dump valve mounted in the discharge port. Because of the corrosive nature of the reactants and the adverse reaction conditions employed, significant difficulties attend the operation of such a valve.
During the period of reaction, the dump valve must seal the opening completely to avoid the loss of chemicals, primarily liquid, under a static head of 20 to 40 tons at high termperatures and varying pressures. For example, in the manufacture of polyvinyl chloride the reactor valve is subjected to temperatures of about 200.degree. F. and pressures ranging between negative pressures, during evacuation of the vessel, and positive working pressures of the order of 150 to 300 pounds per square inch while supporting static heads of over 25 tons.
Under these conditions of operation, it is difficult to maintain a tight seal and efficient operation of the valve, particularly in view of the fact that the discharge port and conduit in which the valve works is a foot or more in diameter, and in view further of the fact that the liquid polymeric product which is discharged may contain solid chunks or may harden into a solid coating that tends to be deposited on the valve plug and the valve seat to prevent tight closure of the valve.